Electrical reduction furnaces have steadily grown in size over the years. During the past two decades, the maximum furnace size (expressed in MVA transformer capacity) has roughly doubled in size for 7 years. Furnace sizes will probably continue to increase due to several factors. First, the capital cost per ton of output is lower for the larger furnaces. Secondly, the number of operating personnel is not significantly larger for a large furnace than for a snall furnace, and since the cost of manpower continues to increase, the use of larger furnaces will enable this cost factor to be kept at a minimum. Thirdly, it is anticipated that there will be a continued increase in demand for ferroalloys, which demand must be met by greater production.
The anticipated increase in the size of electric smelting furnaces involves a number of considerations. First, the production capability of these larger units can be as high as about 1000 tons per day. This in turn means that small improvements in the operation of the larger furnaces may result in significant savings in production costs. Secondly, with the anticipated smaller numbers of larger furnaces, it is feasible to spend more money on instrumentation and control for each furnace. Thirdly, these larger furnaces behave sluggishly, and slowly-developing deviations in operating parameters are not easily detected by furnace operating personnel. Therefore, these larger furnaces have more need for automatic control than smaller furnaces.